This invention relates in general to industrial baghouses and more particularly to a baghouse constructed in a manner to permit on line inspection and servicing of the filter bags.
Continuous emphasis on environmental quality has resulted in considerable importance being attached to the control of industrial emissions. One technique which has proven highly effective in controlling air pollution has been the separation of undesirable particulate matter from a gas stream by fabric filtration.
Such filtration is carried out in dust collection apparatus known in the trade as a "baghouse" which operates on the same general principle as an ordinary vacuum cleaner, except on a much larger scale. The baghouse includes a sheet metal housing which is divided by one or more tube sheets into two chambers referred to as plenums. Disposed in openings in the tube sheet are fabric filters. A particle laden gas stream is passed initially into one chamber (dirty air plenum) where dust accumulates on the fabric filters as the gas flows through the fabric into the other chamber (clean air plenum) and out of the unit through an exhaust duct.
Although all baghouses are constructed in accordance with the foregoing principles, there are numerous operational and structural differences among the various types of baghouses. The present invention is directed to a baghouse in which filtration occurs from the outside to the inside of each bag. In this type of baghouse, referred to as an outside bag collector, the dirty and clean air plenums are separated by the tube sheet, and the filter bags are suspended from the tube sheet with each bag having a cylindrical wire cage providing skeletal support.
Maintaining the filter bags in good condition is essential to effective removal of particulate from the process gas. If the bags are worn to the point of developing holes or other flaws, they do not effectively remove particulates and the gas stream is not properly filtered. The need to periodically clean the bags in order to remove built up dust cake is one of the primary causes of bag wear. Such cleaning is most often carried out by directing high pressure air into either the clean air plenum generally or in pulses into the individual bags in order to dislodge the accumulated dust cake. In either case, the high pressure air to which the bags are exposed during the cleaning cycle tends to deform the filter bags relative to their support cages, and such deformation causes the bags to become worn. In addition to the rough treatment resulting from cleaning, the filters are subjected to considerable wear resulting from the direct impingement of particulate matter against the filter fabric. If the baghouse operates in a corrosive and/or high temperature environment, the wear on the bags is accelerated.
Effective maintenance practice requires that the filter bags be regularly inspected and that bags found to be unduly worn be promptly replaced. In the past, inspection and servicing of the filters for a baghouse having a single clean air plenum has required that the entire baghouse be shut down for maintenance. As can be appreciated, this situation is highly undesirable because it increases the down time of the pollution control equipment and detracts from its efficient utilization of the whole process plant.
To permit on-line servicing of the filter bags, a relatively recent development in the industry is to build the baghouse in modules with each module being a substantially complete, yet small baghouse itself. For maintenance, only one module is taken off line for service while the remainder of the modules continue to perform their filtering function. A further description of a modularized baghouse for continuous, 24-hour operation is found in U.S. Pat. No. 4,158,554 of Bundy et al. issued June 19, 1979 and entitled "Apparatus for Filtering Particulate-Laden Gases". Modular baghouses, however, are only suited for processing plants having enormous filtering requirements.
Baghouses built before the advent of modular style construction and those used in conventionally sized processing plants still have a single, common clean air plenum serving all the filter bags in the unit. There is a need for a baghouse having a single clean air plenum in which maintenance work on the filters can be carried out with the baghouse remaining on line and operating effectively. It is a primary goal of the present invention to provide such a baghouse.
More specifically, it is an object of the invention to provide, in a baghouse having a negative pressure or pull through air handling system, a method and apparatus for selectively isolating service compartments in a single clean air plenum so that on line servicing can be carried out on the filters in the isolated compartments. In accordance with the invention, each service compartment can be isolated from the rest of the clean air plenum by inserting slide gates through normally sealed slots formed in the top of the baghouse. This manner of isolating the service compartments allows all of the filter bags within an isolated compartment to be safely inspected in systematic fashion while the baghouse is on line and without presenting a significant impediment to the flow of process gas through the baghouse. At the same time, the introduction of excessive complexity into the baghouse construction is avoided.
Another object of the invention is to provide, in a baghouse of the character described, simple and effective seal assemblies which normally seal the slots and which can be quickly and easily removed and replaced during the course of the bag servicing operation.
An additional object of the invention is to provide, in a baghouse of the character described, a guide arrangement for properly guiding the slide gates into the clean air plenum and maintaining them in position to enclose the compartment which is to be serviced.
A further object of the invention is to provide a baghouse of the character described which controls leakage and the amount of ambient air that is drawn into the baghouse during the bag servicing operation.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.